1. Field of the Invention
The present invention relates to a coating apparatus.
2. Description of Related Art
A coating line for automotive vehicles generally comprises a coating step for coating vehicle bodies and so on with a paint and a baking step for baking and drying the paint coated on the vehicle bodies in the coating step. Further, when such a paint as, for example, a thermosetting paint is employed, the coating line is provided with a setting step between the coating step and the drying step, in which the paint coated thereon is allowed to be dried at an ambient temperature or at a temperature which is somewhat higher than the ambient temperature.
U.S. Pat. No. 4,874,639, U.S. patent application Ser. No. 323,237 now U.S. Pat. No. 4,919,977, and Japanese Patent Unexamined Publication (kokai) No. 178,871/1988 disclose a coating method in which vehicle bodies and so on are to be sprayed in the coating step with a paint in a film thickness thicker than a film thickness that causes sagging unless the coat formed on the vehicle bodies and so on is treated for preventing sagging and in which the vehicle bodies and so on are rotated at an approximately horizontal axis in a longitudinal direction of the body or the like. This coating method permits the paint to be coated thereon in a film thickness thicker than conventional coating methods could ever achieve, while preventing the coated paint from sagging. Hence, this coating method can provide highly improved flatness on the coat surface. In practically applying this coating method to the coating line for automotive vehicles, the coating method requires the use of such a carriage or carrier for conveying the vehicle bodies or the like through the coating line, as having the construction as described in the above-mentioned prior patent and patent applications. The carriage or carrier has a rotating device built thereon, which can rotate the vehicle body or the like with the coat of the paint formed thereon, while being rotated about its approximately horizontal axis in the longitudinal direction thereof. This kind of carriage or carrier will sometimes be referred to as a rotating carriage or carrier in the description of this specification which follows. The vehicle body and other coating substrate is coated or sprayed with a paint in a film thickness than its sagging limit in the coating step and then conveyed by the coating carriage into the drying step. It should be noted that the terms "sagging limit" and so related to this expression is intended herein to mean a film thickness thicker than a thickness of the paint that sags when a coat of the paint is stayed for a predetermined period of time as it was sprayed. The substrate coated with the paint in such a thick coat thickness may be transferred to the setting step in accordance with the kind of the paint. The coated substrate is then conveyed by the rotating carriage through a baking oven, thereby baking and drying the coat on the substrate. It is further to be noted that approximately 35 minutes are required for baking and drying the vehicle body and so on for one automotive vehicle as well as for heating the automotive vehicle body itself. Hence, on an industrial scale, an oven for baking and drying the vehicle bodies and so on should become extremely longer. Further, a great number of rotating carriages is required. It should be noted herein that the carriage or carrier with the rotating device as described in the prior patent and patent application is much more expensive than usual carriages or carriers. This means that a vast amount of money is required for investment and at the same time such a vast amount of investment naturally leads to a rise in cost. Therefore, further improvements have been demanded to more economically employ the baking oven and the rotating carriages as well as to reduce the number of rotating carriers.